This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/JP00/04072 which has an International filing date of Jun. 21, 2000, which designated the United States of America.
The present invention relates to a technique for manufacturing a three-dimensional structure to be used for a radio wave shield of an electronic device or the like through three-dimensional working for a metal plate, and furthermore, to a metal plate structure therefor.
Various methods have been proposed for manufacturing a shield housing for shielding a radiated radio wave (electromagnetic wave) generated from an electronic device such as a cathode-ray tube by using three-dimensional working for a metal plate.
For example, there has been a method of fabricating a box-shaped shield housing by cutting a development of the shield housing out of a metal plate and bending a boundary line portion of the development and then bonding a junction portion with a rivet, a screw or the like. However, this method has a problem in that the number of steps is necessarily increased and a dividing loss is caused by cutting out the development.
On the other hand, there has been proposed a method of manufacturing a three-dimensional structure by extruding a part of a metal plate through press working to form a projection. According to such a method, the above-mentioned problem does not arise. In this method, however, there is a problem in that it is hard to maintain a very large amount of extension such that the projection has a height of 5 cm or more, for example.
Japanese Patent Publication No. Sho 56-15160 has proposed an improved method of increasing the amount of extension by making the most of the advantages of the above-mentioned method, that is, the three-dimensional extension working of the metal plate. In this method, a large number of cuts are previously provided concentrically like a zigzag in a shield portion (an extension portion) between an inner peripheral edge (a non-extension portion) and an outer peripheral edge (a non-extension portion) of a metal plate to be a metallic flat plate. By stretching both edges to be separated from each other, the shield portion is extended to form a three-dimensional structure. At this time, each cut is expanded to be a meshed portion. According to such a method, a height of the extended shield portion can be set to 5 cm or more, for example.
However, the improved method has a new problem due to the provision of many zigzag cuts in the extension portion of the metal plate. This respect will be described below with reference to FIGS. 9 and 10.
FIG. 9 is an enlarged plan view showing a part of a boundary portion of a non-extension portion PAP and an extension portion PCP of a metal plate which has not been extended, and the designation 2P denotes a cut. Moreover, FIG. 10 is an enlarged plan view showing a part of a boundary portion of a non-extension portion PAP1 and an extension portion PCP1 of the metal plate which has been extended, and the designation 2P1 denotes a cut obtained after the extension. As shown in FIG. 9, the metal plate is basically extended in a direction of an arrow b in the ordinary extension. As a result, the extension portion PCP1 is apt to be contracted in a direction of an arrow a (in a transverse direction of the drawing) as shown in FIG. 10. Therefore, a strain is generated in a boundary portion of the portion PAP having no cut which does not need to be extended and the portion PCP to be extended and the non-extension portion PAP1 of the three-dimensional structure thus formed is wrinkled. For this reason, there is a problem in that a step of smoothing out the wrinkle generated in the non-extension portion PAP1 by using a roller or the like is further required after the extension.
The present invention has been made in order to solve the above-mentioned problems and has an object to prevent a boundary portion of an extension portion and a non-extension portion from being contracted due to generation of a wrinkle in the non-extension portion when three-dimensionally extending a metal plate having a cut to manufacture a three-dimensional structure.
A first aspect of the present invention is directed to a metal plate to be used for manufacturing a three-dimensional structure through three-dimensional extension, comprising a first portion which does not have cuts at all, a second portion connected to the first portion, and a third portion connected to a portion in the second portion on an opposite side of a boundary line of the first portion and the second portion and having the cuts arranged like a zigzag in a first direction parallel with the boundary line, the second portion comprising a plurality of connecting portions extended in a second direction orthogonal to the first direction on the same plane and connecting a portion in the second portion on the boundary line side and the third portion, and a plurality of openings arranged in the first direction, each of which is interposed between connecting portions adjacent to each other out of said plurality of connecting portions.
A second aspect of the present invention is directed to the metal plate according to the first aspect, further comprising a fourth portion which is connected to a portion in the third portion on an opposite side of a connecting portion of the second portion and the third portion, and a fifth portion which is connected to a portion in the fourth portion on an opposite side of a connecting portion of the third portion and the fourth portion and does not have the cuts at all, wherein the plurality of connecting portions and the plurality of openings in the second portion are defined as a plurality of first connecting portions and a plurality of first openings, respectively, the fourth portion comprises a plurality of second connecting portions extended in the second direction and connecting the opposite side portion of the third portion to a portion in the fourth portion on a boundary line side of the fourth portion and the fifth portion, and a plurality of second openings arranged in the first direction, each of which is interposed between second connecting portions adjacent to each other out of the plurality of second connecting portions.
A third aspect of the present invention is directed to the metal plate according to the second aspect, wherein the plurality of first connecting portions are provided at an equal pitch, an end on the third portion side of each of the copy first connecting portions is positioned above a central part of an edge in the first direction of a first cut which is the closest to the opposite side portion of the second portion out of the cuts, the plurality of second connecting portions are provided at an equal pitch, and an end on the third portion side of each of the plurality of second connecting portions is positioned above a central part of an edge in the first direction of a second cut which is the closest to the connecting portion of the third portion and the fourth portion out of the cuts.
A fourth aspect of the present invention is directed to the metal plate according to the third aspect, wherein a shape of each of the plurality of first connecting portions is a rectangular parallelepiped, a sectional shape of each of the plurality of first openings is a rectangle, a shape of each of the second connecting portions is a rectangular parallelepiped, and a sectional shape of each of the plurality of second openings is a rectangle.
A fifth aspect of the present invention is directed to a method of manufacturing a three-dimensional structure, comprising the steps of preparing the metal plate according to the third aspect, and extruding the fifth portion of the metal plate in a third direction orthogonal to the first direction and the second direction to extend the cuts, thereby processing the third portion into a meshed portion.
A sixth aspect of the present invention is directed to a three-dimensional structure manufactured by the method of manufacturing a three-dimensional structure according to the fifth aspect.
A seventh aspect of the present invention is directed to an electronic device comprising an electronic device body, and a radio wave shielding member constituted by the three-dimensional structure according to the sixth aspect.
According to each of the first aspect and the fifth to seventh aspects of the present invention, even if the third portion of the metal plate utilizing the cut is extended, a strain generated by the extension can be absorbed by the connecting portion and the opening in the second portion. Therefore, it is possible to inhibit a wrinkle from being generated in the first portion to be the non-extension portion, thereby preventing the boundary portion of the first portion and the extension portion from being deformed unnecessarily.
According to each of the second aspect and the fifth to seventh aspects of the present invention, even if the third portion of the metal plate utilizing the cut is extended, a strain generated by the extension can further be absorbed by the connecting portion and the opening in the fourth portion. Therefore, it is possible to inhibit a wrinkle from being generated in the fifth portion to be the non-extension portion, thereby preventing the boundary portion of the fifth portion and the extension portion from being deformed unnecessarily.
According to each of the third aspect and the fifth to seventh aspects of the present invention, the third portion can be extended such that each cut is a meshed portion having the same shape.
According to each of the fourth aspect and the fifth to seventh aspects of the present invention, it is possible to easily form the connecting portion and the opening in each of the second and fourth portions.